Triglycerides are one of the major energy storage molecules in eukaryotes. The absorption of triglycerides (also called triacylglycerols) from food is a very efficient process that occurs by a series of steps wherein the dietary triacylglycerols are hydrolyzed in the intestinal lumen and then resynthesized within enterocytes. The resynthesis of triacylglycerols can occur via the monoacylglycerol pathway, which commences with monoacylglycerol acyltransferase (MGAT) catalyzing the synthesis of diacylglycerol from monoacylglycerol and fatty acyl-CoA. An alternative synthesis of diacylglycerols is provided by the glycerol-phosphate pathway, which describes the coupling of two molecules of fatty acyl-CoA to glycerol-3-phosphate. In either case, diacylglycerol is then acylated with another molecule of fatty acyl-CoA in a reaction catalyzed by one of two diacylglycerol acyltransferase enzymes to form the triglyceride (Farese et al., Curr. Opin. Lipidol., 2000, 11, 229-234).
The reaction catalyzed by diacylglycerol acyltransferase 1 is the final and only committed step in triglyceride synthesis. As such, diacylglycerol acyltransferase 1 is involved in intestinal fat absorption, lipoprotein assembly, regulating plasma triglyceride concentrations, and fat storage in adipocytes. Although identified in 1960, the genes encoding human and mouse diacylglycerol acyltransferase 1 (also called DGAT1, acyl CoA:diacylglycerol acyltransferase, acyl CoA:cholesterol acyltransferase-related enzyme, ACAT related gene product, and ARGP1) were not cloned until 1998 (Cases et al., Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 13018-13023; Oelkers et al., J. Biol. Chem., 1998, 273, 26765-26771). U.S. Pat. No. 6,100,077 refers to an isolated nucleic acid encoding a human diacylglycerol acyltransferase 1. Diacylglycerol acyltransferase 1 is a microsomal membrane bound enzyme and has 39% nucleotide identity to the related acyl CoA:cholesterol acyltransferase (Oelkers et al., J. Biol. Chem., 1998, 273, 26765-26771). A splice variant of diacylglycerol acyltransferase 1 has also been cloned that contains a 77 nucleotide insert of unspliced intron with an in-frame stop codon, resulting in a truncated form of diacylglycerol acyltransferase 1 that terminates at Arg-387 deleting 101 residues from the C-terminus containing the putative active site (Cheng et al., Biochem. J., 2001, 359, 707-714).
Dysregulation of diacylglycerol acyltransferase 1 may play a role in the development of obesity. Upon differentiation of mouse 3T3-L1 cells into mature adipocytes, a 90 fold increase in diacylglycerol acyltransferase 1 levels is observed. However, forced overexpression of diacylglycerol acyltransferase 1 in mature adipocytes results in only a 2 fold increase in diacylglycerol acyltransferase 1 levels. This leads to an increase in cellular triglyceride synthesis without a concomitant increase in triglyceride lipolysis, leading to the suggestion that manipulation of the steady state level of diacylglycerol acyltransferase 1 may offer a potential means to treat obesity (Yu et al., J. Biol. Chem., 2002, 277, 50876-50884).
Alterations in diacylglycerol acyltransferase 1 expression may affect human body weight. In a random Turkish population, five polymorphisms in the human diacylglycerol acyltransferase 1 promoter and 5′ non-coding sequence have been identified. One common variant, C79T, revealed reduced promoter activity for the 79T allele and is associated with a lower body mass index, higher plasma cholesterol HDL levels, and lower diastolic blood pressure in Turkish women (Ludwig et al., Clin. Genet., 2002, 62, 68-73).
Diacylglycerol acyltransferase 1 knockout mice exhibit interesting phenotypes which indicate that inhibition of diacylglycerol acyltransferase 1 may offer a strategy for treating obesity and obesity-associated insulin resistance. Mice lacking diacylglycerol acyltransferase 1 are viable and can still synthesize triglycerides through other biological routes. However the mice are lean and resistant to diet-induce obesity (Smith et al., Nat. Genet., 2000, 25, 87-90), have decreased levels of tissue triglycerides, and increased sensitivity to insulin and leptin (Chen et al., J. Clin. Invest., 2002, 109, 1049-1055).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of diacylglycerol acyltransferase 1 and to date, investigative strategies aimed at modulating diacylglycerol acyltransferase 1 function have involved naturally-occurring small molecule derivatives of roselipins and xanthohumols isolated from Gliocladium roseum and Humulus lupulus, respectively (Tabata et al., Phytochemistry, 1997, 46, 683-687; Tomoda et al., J. Antibiot. (Tokyo)., 1999, 52, 689-694).
Consequently, there remains a long felt need for additional agents capable of effectively inhibiting diacylglycerol acyltransferase 1 function.